1. Field of the Invention
The present invention relates to a projection apparatus, adapted for use for example in a color liquid crystal projector which projects image information, displayed on an optical modulating element such as a color liquid crystal display panel, onto a screen in a magnified manner.
2. Related Background Art
There have been proposed various color liquid crystal projectors, which projects the optical information, displayed on a liquid crystal panel serving as an optical modulating element, onto a screen. Among such projectors, an optical system for use in a liquid crystal projector employing a transmissive liquid crystal apparatus is disclosed for example in the Japanese Patent Laid-open Application No. 61-99118. FIG. 28 is a schematic view of the optical system proposed in the above-mentioned patent application.
Referring to FIG. 28, the light emitted from a light source 1 is converted by a reflector (parabolic mirror) 2 into a substantially parallel light beam, which then enters a dichroic mirror 34 transmitting the green (G) light and reflecting the green (G) and red (R) lights. The G and R lights reflected by the dichroic mirror 34 enters a dichroic mirror 35, which reflects the green (G) light and transmits the red (R) light. The G light beam reflected by the dichroic mirror 35 illuminates a liquid crystal panel 14 for the G light while the R light beam transmitted by the dichroic mirror 35 illuminates a liquid crystal panel 15 for the R light. Also the blue light beam transmitted by the dichroic mirror 34 illuminates, via mirror 36, a liquid crystal panel 16 for the B light. The light beams transmitted by the liquid crystal panels 14, 15, 16 are respectively modulated by the image information of respective colors. The light beams from the liquid crystal panels 14, 16 are synthesized by a dichroic mirror 37 which transmits the blue light beam and reflects the green light beam. Also the red light beam from the liquid crystal panel 15 enters, via a mirror 38, a dichroic mirror 38 which transmits the red light beam and reflects the blue and green light beams.
The red, blue and green light beams are synthesized by the dichroic mirror 39 to provide a full color image, which is projected through a projection optical system 22 onto a screen 23. In the liquid crystal panels 14, 15, 16 there is employed, for example, twisted nematic (TN) liquid crystal or super-twisted nematic (STN) liquid crystal.
FIG. 29 is a schematic view of an optical system for a color liquid crystal projector, employing the transmissive liquid crystal apparatus, as proposed in the Japanese Patent Laid-open Application No. 1-131593.
Referring to FIG. 29, the light emitted from a light source 1 is converted by a reflector (parabolic mirror) 2 into a substantially parallel light beam, which then enters a dichroic mirror 341 reflecting the blue (B) and transmitting the green (G) and red (R) lights. The light beam transmitted by the dichroic mirror 341 enters a dichroic mirror 35', which transmits the green light and reflects the red light. The green light beam transmitted by the dichroic mirror 35' illuminates a liquid crystal panel 14 for the green light while the red light beam reflected by the dichroic mirror 35' illuminates, via mirrors 38, 41, a liquid crystal panel 15 for the red light. Also the blue light beam reflected by the dichroic mirror 34' illuminates, via mirrors 36, 40, a liquid crystal panel 16 for the blue light.
The light beam transmitted by the liquid crystal panels 14, 15, 16 are respectively modulated by the image information of respective colors, and enter a cross dichroic prism 42 wherein they are synthesized as a full-color image. The cross dichroic prism 42 is composed of a cross-shaped combination of a dichroic mirror transmitting the green light beam and reflecting the blue light beam and a dichroic mirror transmitting the green light beam and reflecting the red light beam. The full-color image synthesized in the cross dichroic prism 42 is projected through a projection optical system 22 onto a screen 23.
FIG. 30 is a schematic view of an optical system for a color liquid crystal projector, employing a reflective liquid crystal apparatus, as disclosed in the Japanese Patent Laid-open Application No. 6-265842. This optical system is called a Schlieren optical system.
Referring to FIG. 30, the light emitted from a light source 1 is converted by a reflector (parabolic mirror) 2 into a substantially parallel light beam, then reflected by a mirror 36, and is condensed by a condenser lens 4 so as to form an image of the light source in the vicinity of a mirror 43 positioned at a diaphragm aperture of the projection optical system 22. The light beam reflected by the mirror 43 is emitted toward a plano-convex lens 44, converted therein into a parallel light beam, then separated by a cross dichroic prism 42 into the light beams of three colors which respectively illuminate reflective liquid crystal panels 25, 26, 27 of the respective wavelength regions.
The light beams respectively modulated by the reflective liquid crystal panels 25, 26, 27 are synthesized by a cross dichroic prism 42 into a full-color image, which is condensed by a plano-convex lens 44, then transmitted by a diaphragm 28 and projected through a projection optical system 22 onto a screen 23.
The liquid crystal panel contains, for example, polymer liquid crystal of dispersion type, which becomes transparent in case of displaying a white level, thereby reflecting the light beam, but scatters the light beam in case of displaying a black level. The light reflected by the liquid crystal panels and color synthesized by the cross dichroic prism 42 is condensed by the plano-convex lens 44 in the vicinity of the diaphragm 28 of the projection optical system 22. The light beam reflected by the liquid crystal panel is mostly transmitted by the aperture of the diaphragm 28 and displays the white level on the screen 23 through the projection optical system 22, while the light beam scattered by the liquid crystal panel is transmitted, only by a very limited portion, by the aperture of the diaphragm 28, thereby displaying the black level on the screen 23.
As explained in the foregoing, the light scattering in the liquid crystal is utilized to display the image information, which is projected by the projection optical system onto the screen.
FIGS. 31A and 31B are respectively an entire view and a schematic partial view of a color liquid crystal projector proposed in the Japanese Patent Laid-open Application No. 4-428, wherein liquid crystal panels 14, 15, 16 are respectively illuminated with the R, G and B lights. The light beams from the liquid crystal panels, illuminated with the respective color lights are condensed by auxiliary lenses 17, 18, 19 in the vicinity of the entrance pupil EnP of a projection lens 30. The light beam from the auxiliary lens 18 is directly entered into a projection optical system 22, while that from the auxiliary lens 17 is guided thereto via a mirror 20, and that from the auxiliary lens 19 is guided thereto via a mirror 21. The projection optical system 22 projects images, displayed on the liquid crystal panels 14, 15, 16 onto a screen 23.
In FIGS. 31A and 31B, there are illustrated principal rays Pr1, Pr2, Pr3 at the center for the respective projection systems, and three rays for each of the projection systems. The optical axis of the auxiliary lens 18 of the central projection system B coincides with that of the projection lens 32, and the optical axes of the auxiliary lenses 17, 19 of the peripheral projection systems A, C are perpendicular to the optical axis of the projection lens.
The entrance pupil EnP of the projection lens is positioned at the crossing point of the optical axes of the three auxiliary lenses, and the mirrors 20, 21 are so positioned that the end points thereof at the center side coincide with the entrance pupil EnP and are inclined by 45.degree. with respect to the optical axis of the projection lens 32.
In the central projection system B, the liquid crystal display panel is so positioned that the central axis thereof coincides with the optical axis of the auxiliary lens 18, while, in the peripheral projection systems A and C, the liquid crystal display panels are so positioned that the central axes thereof are shifted toward the left-hand side in the drawings, with respect to the optical axes of the respective auxiliary lenses.
Consequently the principal ray Pr2 of the central projection system B passes the optical axis of the projection optical system 22 and becomes perpendicular to the screen 23, while the principal rays Pr1, Pr3 of the peripheral projection systems A, C become oblique to the screen 23. The three principal rays mutually cross on the screen.
FIG. 32 is a schematic view of a color image projection apparatus disclosed in the U.S. Pat. No. 5,108,172, wherein the white light from a lamp 238 is guided, in respective color channels, into corresponding lens means 210 (210', 210"). For example, in the red channel, the white light is condensed by the lens means in the vicinity of an apertured mirror 214, then reflected by the mirror 214, converted into a parallel light beam by a field lens 216 and introduced into a reflective liquid crystal panel 218, and the light bearing the image information, reflected from the panel 218, is condensed by a lens 216 in the vicinity of the mirror 214 in such a manner that the non-scattered light (normal reflected light) in the reflected light passes through the aperture of the mirror 214 while a major portion of the scattered light in the reflected light does not enter the aperture of the mirror 214.
The non-scattered light of the red channel is guided by a mirror 242, reflected to a dichroic mirror 244 and introduced into a dichroic mirror 246. Also the green light is guided, through a similar optical path and through a dichroic mirror 244 and introduced into the dichroic mirror 246, and the blue light is also introduced into the dichroic mirror 246. Then an image represented by the lights synthesized by the dichroic mirrors 244, 246 is displayed by a projection lens 240 onto a screen.
In the image projection apparatus shown in FIG. 32, a color filter is provided in the optical path of each channel, in order to provide the non-scattered light of each color channel with a corresponding color, and, since such color filter absorbs the light of other colors, the major portion of the light emitted from the lamp is wasted. Consequently the efficiency of utilization of the light from the lamp tends to become low, and it is difficult to obtain a bright image.